The present invention relates to rotary compressors. More specifically, the present invention relates to a rotary compressor having a sliding vane positioned in order to reduce noise.
A rotary type of compressor as commonly used for refrigerators and air conditioners often generates high frequency (4 KHz to 10 KHz) noise. Indeed, some refrigerators use rotary compressors which show a strong almost pure-tone noise of about 4 KHz, this being a frequency to which the human ear is most sensitive.
Various methods of reducing rotary compressor noise have previously been considered.
One approach is to redesign the casing of the rotary compressor so as to reduce the sound radiation from it. The noise heard by the human ear results from the vibration of the casing which encloses the whole compressor structure. Modifying the sound radiation pattern is necessary for this approach. The radiation pattern can be modified by changing the bending rigidity of the compressor, i.e., changing the casing thickness or adding stiffness to the casing. However, redesigning the casing is relatively expensive and is therefore undesirable.
Another way of attenuating the compressor noise is by controlling the compressor gas spectrum directly. Any resonator type of device built into the discharge port works as a mechanical filter. This may adversely affect the compressor efficiency depending on the structure of the resonator.
Other attempts to reduce the high frequency noise have included changes in orifice design, clearances, and root radii. These changes have only been partially successful and are somewhat disadvantageous in that they often reduce the efficiency of the compressor.
One of the potential sources for the noise in a rotary compressor is the frictional effect between the vane and the cylinder surfaces which may best be explained by reference to prior art FIG. 1. FIG. 1 shows a simplified view of portions of a rotary compressor 10 including a cylindrical wall 12 and a roller or rolling piston 14 which eccentrically rotates about rotation axis 16. The rotation axis 16 is also a center axis of symmetry of the cylindrical wall 12. The roller 14 has a center axis of symmetry 18 which is offset from the rotation axis 16 to provide for the eccentric rotation. A sliding vane 20 is disposed in a slot 22 in the cylindrical wall 12. The slot 22 includes a close side 24C which is relatively close to a compression chamber 26 and a far side 24F which is relatively far from the compression chamber 26. Most of the noise generated by such a compressor occurs when the roller 14 is in the high pressure portion of its cycle. That is, most of the noise occurs when refrigerant is being compressed in compression chamber 26. A possible cause of the noise or contributing factor to the noise is jamming of the sliding vane 20 against the walls or sides of the slot 22. In particular, the roller 14 applies a force 28 to the vane 20. This force 28 includes a component parallel to the vane center line 20C (which vane center line is radial to the rotation axis 16) and a component perpendicular to the vane center line 20C. (The vane center line 20C of course corresponds to the center of the slot 22 and is the direction of movement of the vane 20.) The component of force 28 normal to the vane center line 20C tends to jam the vane 20 against the side 24F at point 30 and cause high frictional resistance, thus impeding the smooth motion of the vane and generating noise.
Although the above approaches at noise reduction have been somewhat useful, there remains a need for significantly reducing the noise from a rotary compressor without reducing the efficiency of the compressor.